Polycarbonate has found many uses as an engineering thermoplastic because it combines, in general, a high level of heat resistance, impact resistance and dimensional stability with good insulating and non-corrosive properties, and it is easily molded by conventional fabrication processes. It does, however, suffer from a tendency to craze and crack under the effects of contact with organic solvents such as gasoline, especially when under stress such as in flexure, tension or torsion. Polycarbonate which has crazed is, undesirably, more likely to experience brittle rather than ductile failure upon impact. This disadvantage has been somewhat relieved by the practice of blending polycarbonate with various olefin polymers such as polyethylene, polypropylene or polyisobutylene, as described for example in Goldblum, U.S. Pat. No. 3,431,224. However, they can cause delamination of the blended composition, as reported for example in Bussink, U.S Pat. No. 4,122,131.
In U.S. Pat. No. 4,859,738, a solvent-resistant blend of polycarbonate, polyester and ethylene/carbon monoxide copolymer is disclosed. A group of several different elastomeric impact modifiers is set forth therein for use in such blends. We have found unexpectedly that use of a combination of certain of those listed impact modifiers imparts particularly good improvement in impact strength to the polycarbonate blend while maintaining the resistance to solvents.